Magnetic can handling apparatus with surge and hold control

ABSTRACT

Apparatus for transferring patterns of cans from a pallet to a conveyor includes a carriage having can lifting electromagnets. The magnets are powered from a silicon controlled rectifier bridge and successive control signals are sent to the bridge upon magnet energization. First a relatively high current &#39;&#39;&#39;&#39;surge&#39;&#39;&#39;&#39; signal is provided for initially gripping the cans, after which a timer relay circuit replaces the surge signal with a lower current &#39;&#39;&#39;&#39;hold&#39;&#39;&#39;&#39; signal.

United States Patent Inventor Peter L. Chorney l-loopeston, Ill.

Appl. No. 845,371

Filed July 28, 1969 Patented Aug. 17, 1971 Assignee FMC Corporation San Jose, Cnlil.

MAGNETIC CAN HANDLING APPARATUS WITH 294/655; 317/154, DIG. 4

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[56] Relerences Cited UNITED STATES PATENTS 3,241,002 3/1966 Smith 312/123 CD 1,915,566 6/1933 Younghusband... 294/655 X 2,071,859 2/1937 Steiner 214/1 (BS2) X 3.036345 5/1962 Fourey l 294/655 X Primary Examiner-Gerald Mt Forlenza Assistant Examiner-George F. Abraham Anorneys- F. W. Anderson and C. E. Tripp S sen-2 01 DZ T1 1G2. 1 I H (+1 1 04 r BCTR-S 0 Ben L -4 DEENERGIZED ecR-s R2 Sui-3 U No 172. L651 -cuT OFF sum um:

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SHEET 9 OF 9 m-m-hr 380: 02.5. mom @252; 6528 MAGNETIC CAN HANDLING APPARATUS WITH SURGE AND HOLD CONTROL SUMMARY OF THE INVENTION This invention relates to the magnetic handling of articles such as tin cans or the like and is disclosed in a system for transferring articles between a pallet hoist and a conveyor, such as a depalletizer. In handling systems of this type, a pattern of cans is picked up by a magnetic head and deposited upon deenergization of the magnets. These cans are generally loaded on pallets in tiers and cans at the edges of the patterns may be tipped or inclined slightly. Also, the chimes or beads of the cans may be interlocked so that all of the tops of the cans do not lie in the same plane.

When a pattern of cans is presented to an electromagnetic transfer head, cans which are tilted or are otherwise not in the general plane of the can tops will not be intimately seated against the magnets and hence may be dropped or may remain in a misaligned position. If a magnetic head is provided which operates normally at a flux density strong enough to straighten out tilted cans and to pull rim locked cans against the magnets, then such a magnetic head will be over designed. That is, it will be of a larger capacity than that required for the further handling of the cans once they are gripped by the magnets. It is well known that it requires a considerably stronger flux to pull a magnetic article against a magnet than to hold it there once it is in contact with a magnet, due to the elimination of the air gap in the circuit.

On the other hand, if a magnetic head is designed of adequate size and current capacity for transporting cans that are firmly against the head, then such a head will not always be eflective to align tilted cans and to insure a firm gripping of rim locked cans. If the above-type "normal" design magnetic head is supplied with additional current to increase the flux density of the magnetic field, the magnets will heat up excessively resulting in poor electrical efficiency and short life.

In accordance with the present invention, the magnets need not be overdesigned and can operate at a normal current for the design, and yet tilted and rim locked cans are gripped and pulled into engagement with the magnetic pole pieces, thereby insuring formation of precise patterns and the pickup of all cans in the pattern by the magnetic head. Under the present condition, the increased current for magnetic can pickup referred to as a "surge" current is applied only for a short time, namely a few seconds, after which the current is automatically switched to a normal operating or "hold" current by an automatic timer circuit. Since the larger surge current is applied to the magnets only for a matter of seconds, it does not significantly increase the heat generated in the magnets, which are designed to withstand the heat generated therein by the normal or "hold" current. In most operations even the "hold" current is turned off while the carriage or the like that mounts the magnets is moved from the position of can deposit to the position of can pickup, so that ample cooling time is provided for the magnets under the present invention even though their rating is, in effect, greatly increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a pallet hoist unloader embodying the present invention.

FIG. IA is an enlarged fragmentary view of a signal switch.

FIG. 15 is an enlarged fragmentary section of a magnet.

FIG. 2 is a plan view of the unloader.

FIG. 3 is an end view of the unloader with portions being broken away.

FIG. 4 is a plan of the carriage with portions being broken away.

FIG. 5 is a central vertical section taken on line 5-5 of FIG. 4.

FIG. 6 is a fragmentary plan of the magnet blade switch.

FIG. 7 is a side view of the magnet blade switch.

FIGS. 8- 10 are electrical diagrams showing an operational sequence.

GENERAL DESCRIPTION OF THE UNLOADER FIGS. 1-5 show in simplified form a pallet unloader L embodying the present invention. The principle components of this unloader have counterparts in a pallet loader-unloader previously manufactured by the FMC Corporation, and identified as the Stackmatic Pallet Unloader, the device of the present invention being an improvement in the prior machine. Except for the motor drive for the conveyor, the elements are controlled hydraulically. Actually the machine as manufactured and sold has automatic switch and interlock devices so that it is self-sequencing. Generally speaking, the automatic sequencing features of the device (being known and conventional) are neither critical nor essential to the present invention. Thus, in order to distinctly describe and point out the invention in this case, the hydraulic cylinders, pumps, sequencing switches, solenoid valves, etc. are illustrated in their simplest diagrammatic form, and instead of showing an automatic control circuit for the operating cylinders, simple pushbuttons are indicated. The features of the present invention cannot only be employed in a pallet unloader (as illustrated) but can be employed in a pallet loader such as that shown in the copending U.S. application of Forshier et al., Ser. No. 746,568, filed July 22, I968 now U.S. Pat. No. 3,493,126 and assigned to the FMC Corporation.

The basic elements of the unloader L include an endless draper conveyor 20 and a magnetic pickup head M mounting a series of electromagnets I2. The magnetic head is mounted on a reciprocating carriage C that moves between pallet overlying and conveyor overlying positions. Associated with the unloader is a pallet hoist H, which raises a pallet P loaded with tiers of cans I0 up to a can unloading position and which successively raises the pallet after each tier or pattern of cans 10 has been removed from the pallet for deposit on the conveyor 20. For convenience a pallet conveyor K, which is of conventional design, runs along the pallet hoist end of the machine, for supplying loaded pallets to the hoist platform and for facilitating removal of empty pallets therefrom.

The unloader has a frame that includes carriage tracks I4 (FIG. 3) supported on front legs 16 and rear legs I7 (FIG. 1). Various frame crosspieces are provided. The conveyor 20 includes a draper belt 22 that is trained around an idler pulley 24 and a drive pulley 26. The conveyor delivers cans 10 to a singulating turntable 28 (FIG. 2) which is surrounded by a fence 29 having a singulating discharge mouth 30. The conveyor belt 22 normally runs continuously and advances patterns of cans as they are deposited on the conveyor to the singulator turntable 28. The details of the singulator are not es sential to the invention.

The conveyor 20 is driven by a motor 32 having a gear box 34 (FIG. 1) with a drive pulley 36 that drives the pulley 26 of the conveyor by a V-belt chain 38. The gear box 34 also drives a vertical shaft 42 (FIG. I) which rotates the turntable 28 (FIG. 2). The nature of the conveyor drive is not critical to the present invention so long as it can be reversed in case the machine is to be employed as a pallet loader.

CARRIAGE The carriage C, which mounts the magnetic pickup head M, reciprocates from a can pickup position over the pallet P (solid lines in FIG. 1) to a can release position over the pallet P (solid lines In FIG. I) to a can release position over the conveyor 20 (broken lines). The carriage has a rectangular framework 50 (FIG. 4) with four depending legs 52 mounting rollers 54 that reciprocate in the guide channels I4 on the frame. A U-shaped vertically adjustable sub frame 56 is suspended from the main carriage frame 50 by means of four threaded adjustment rods 58. The rods 58 are rotatably mounted in the main carriage frame 50 and are threaded in nuts or the like 60 welded to the subfrarne 56 as best seen in FIG. 3. The upper ends of the rods 58 carry sprockets 62 which are all connected by a chain 64 and one of the threaded rods 58 can be rotated by a handle 66 (FIG. 4) thereby simultaneously turning all of the threaded rods and raising or lowering the subframe $6. This adjustment is provided to accommodate cans of various heights.

The magnets 12 can be independently raised and lowered by a hydraulic cylinder assembly, but during the unloading operation this assembly is actuated to raise the magnets to their uppermost position and left there, which is the position shown in the drawings. However, the magnets 12 are supported only by gravity in a manner whereby they can be raised to a limited extent by the lifting action of the pallet hoist, in order to operate parallel connected signal switches the purpose of which will be described presently.

The magnets are suspended from the subframe S6 previously described by means of crossbars 70, the ends of which rest on and are supported by the subframe 56 as seen in FIGS. 3 and 4. The crossbars 70 are welded to longitudinal rails 72 and these rails are bridged by a central channel 74 which mounts the hydraulic magnet raising cylinder 76 previously referred to.

The magnets 12 are bolted to angles 80 which run parallel to the angles 72 just described (FIG. 4). In order that the hydraulic cylinder 76 can raise and lower the magnets during the loading operation as described in the aforesaid copending application of Forshier et al., the magnet mounting angles 80 are connected by crosspieces 82 (FIGS. 3 and 4) and the crosspieces are joined by central lifting brackets 84 which run parallel and are closely spaced. The piston rod 86 of the cylinder 76 (FIG. 3) has secured at its upper end a bracket 88 (see also FIG. 4) from which depend vertical rods 90 that are pinned to the crosspieces 84. As mentioned, during the loading operation the hydraulic cylinder 76 is actuated so that the piston rod lifts the magnets 12 up against the lower surfaces of the angles 72 and holds them there. However, the magnet assembly, including the magnets 12 and the framework elements 70, 72 which mount the piston 76 can all be lifted as a unit by the pallet hoist through a distance great enough to operate parallel connected signal microswitches LS-l at opposite cornets of the framework (FIG. 4). This operation of the limit switches LS-I by the raising of the magnet assembly appears in FIGS. IA and and the operation of either switch lights a signal lamp S. This shows that the pallet hoist has been raised sufficiently to bring a pattern of cans up against the magnets so that when the magnets are energized all cans will be picked up and also indicates that raising of the pallet hoist should stop.

As seen in FIG. 1B, the magnets 12 are elongate rectangular bars formed to provide a three pole electromagnet. The magnets are formed of channels 12a to which a center pole piece I2b is screwed and the windings [2c are wrapped around the center pole piece. The windings 12c of the magnets are usually connected in a seriesparallel arrangement in accordance with the voltage supplied to the magnets, the size of the windings and the desired current load for the magnets. Details of the number of windings. wire size and the dimensions of the pole pieces are not essential to the present invention. these being matters of electrical engineering which can be determined for a given size of pattern and weight range of cans to be handled.

The carriage C is reciprocated between its advanced position over the pallet hoist and its retracted position over the conveyor by a pair of hydraulic cylinders 92 (FIGS. l3) having piston rods 94 that connect to carriage-mounted brackets 96. A limit switch LS3 (FIG. 1) is operated upon the retraction of the carriage by a switch operator button 98 on one of the brackets 96 that mount the piston rod 94. The function of LS-J is to deenergize the magnets for can release.

PALLET HOIST In order to receive the tiers of pattern cans, the pallet hoist H is disposed between the conveyor sections K (FIGS. 2 and 3) and is beneath the magnetic head M (FIGS. 1 and 2) when the carriage C is in its advanced position. The details of this hoist are not critical to the present invention and hence the Llt hoist is illustrated diagrammatically. The pallets P rest on a hoist carriage 100 which can be lowered between the conveyor sections K to receive a pallet load of cans and then incrementally raised by one can height, afier each tier of cans is removed from the pallet.

The hoist carriage 100 (FIGS. 1 and 3) is mounted on rollers 102 which slide on vertical tracks 104 forming a portion of the framework of the apparatus. The hoist carriage is raised and lowered by a frame-mounted hydraulic cylinder I06, having a piston rod 108 that supports a crosshead 110. The crosshead mounts a sprocket shaft 112 carrying sprockets 113 over which are trained lifting chains 114. The chains themselves have one end anchored to the frame at 116 and the other to the hoist carriage at 118 (FIG. 1). Thus raising or lowering the piston rod 108 and the crosshead 112, raises or lowers the hoist carriage 100 by twice the piston travel.

As seen in FIG. 3, the pallet hoist K has a pallet delivery section 120 and a loaded pallet take away section 122. An intermediate section 124 of the pallet conveyor is spaced from the delivery and take away sections to accommodate the hoist carriage arms 126, when the latter are lowered. Thus pallets can be advanced from the delivery section onto the intermediate section with the carriage arms in their lowered positions, and lifting of the carriage arms by the hydraulic cylinder I06 will raise the pallet and bring it up toward the magnetic head M for unloading.

CONTROLS The hydraulic piston 76 for raising and lowering the magnetic head M is controlled by a four-way solenoid valve (FIG. 1). This valve is connected to a source of hydraulic fluid in a conventional manner, the details of which are not critical to the invention. A manual control of the parts not critical to the invention is disclosed herein. Thus, the solenoid valve I30 for the magnet piston may be raised and lowered by a switch 132 that operates the valve. This assembly is only used during loading, as explained in the aforesaid copending application.

The hoist cylinder 106 is controlled by a solenoid valve 134 (FIG. I) and a raise and lower switch 136 that is manually operated. As previously explained, when the hoist has been raised sufficiently to fully seat a pattern of cans against the magnet, limit switches LS-l are opened (FIG. 1A) which lights the signal lamp S and indicates that raising of the pallet hoist should be stopped by the control switch I36.

The hydraulic cylinders 92 that advance and retract the carriage C for the magnetic head are operated in parallel by conventional hydraulic techniques not shown in detail. The cylinders are simultaneously advanced or retracted by means of a solenoid valve 140 (FIG. 1) controlled by an advance and retract pushbutton 142. As mentioned, when the carriage C is fully retracted it opens the limit switch LS-3. The extremes of carriage motion are mechanically determined by stops in a convention manner.

As part of the magnet energizing and deenergizing circuit a limit switch LS-Z (FIGS. 6 and 7) is mounted on one of the crosspieces 82 and forms part of the magnetic head. This limit switch is operated by a blade that is pivoted to the crosspiece 82 at I52 and which moves up and down between a pair of magnets 12. When no cans are against the magnets, the lower portion of the blade 150 projects downwardly but when cans are brought up against the magnet by the pallet P and the hoist, the blade ISO is raised, operating the limit switch LS-2 for energizing the magnets, as will be described presently.

GENERAL DESCRIPTION OF THE CONTROL CIRCUIT Before describing the operation of the control circuit, reference is made to FIG. 8 for a general description of the major elements thereof. In the embodiment shown, the loader is powered from an alternating current source AC An SCR firing module F is connected to the AC source and contains a saturable core control winding of a magnetic amplifier which is part of the module. This module controls a rectifier bridge incorporating two silicon controlled rectifiers SCR-1 and SCR-2 and two diodes DI and D2. The output of the bridge being positive and negative lines DC lines I60, I62 respectively. The details of the SCR firing module are not critical to the present invention and such items are supplied to the trade by a number of manufacturers. A suitable example of the SCR firing module and bridge is the CL-78l or CL-782 firing circuit module manufactured by Crydom Laboratories, Inc. of Santa Ana, Calif., and described in their published brochure Crydom SCR Firing Circuit Modules" which is distributed to the trade. Firing modules for bridges of this type are also described in Bulletin 500] of June I967 published by Firing Circuits, Inc., a Division of Marathon Electric Manufacturing Corporation of Norwalk, Conn. The title of this bulletin is "SCR Controls, and FIGS. I and 13, pages 4 and 5 are pertinent. Another firing circuit which can be utilized is described in the US. Pat. No. 3,386,026, to Gutterman May 28, I968.

The DC power lines 160, I62 energize the magnets M and can be shorted in the direction of magnetic field collapses by a silicon controlled rectifier SCR-3 connected across the DC line. In order to supply a DC control voltage for the control winding of the SCR firing module F, an isolation step down transformer T-I is connected across the AC line and supplies rectified DC voltage between positive and negative lines 164, I66 respectively. This rectified direct current is obtained from the transformer T1 the secondary of which is center tapped and diodes D3, D4 in accordance with conventional electrical engineering practice. A filter capacitor CI smoothes out the control current, which may be supplied at about 6 to 8 bolts.

A series resistor RI and a Zener diode D5 across the control line limits the controlled current to a predetermined maximum value such as 8 volts. A normally open relay contact 3CR-l is in the DC line I64. In this general discussion of the circuit, it will be noticed that there are relays and relay controlled switch contacts, the function of which will be best understood in the sequential operation of description of the circuit which follows. Accordingly, for the present, no full explanation of the relay switch contacts is presented.

Under the present invention, a limit rheostat R3 is in the positive DC control line I64 and supplies current to paralleled potentiometers that provide either of two control currents in accordance with the present invention. These potentiometers are a "hold potentiometer R4 and a surge" potentiometer R5, each of which is connected through respective relay timing contacts (JCR-Z, normally open but timed to close and 3CR-3, normally closed but timed to open) to one side I68 of the control line leading to the lining SCR firing module F. The other side 170 of the control line returns to the center tap of the power supply and isolation transformer TI previously mentioned.

In accordance with the invention of Albright et al. Ser. No. 845,45], filed July 28, I969 (SJ 54l5), a silicon controlled rectifier clamping SCR-3 is connected across the magnets and its gate is connected to the positive DC control source line I64 by a line I72 through a current limiting resistance R2. The gate can also be connected by a relay contact SCR-3 to the return line 166 of the DC control source. These connections either fire the silicon controlled rectifier SCR3 or permit it to cut ofl when the collapse current through the magnets falls below the rated holding current of the rectifier (e.g. 5-200 ma.) However, even if the magnetic field collapse current were to fall to zero, residual magnetism would remain.

In accordance with the Albright et al. invention, the operation of the field collapse rectifier SCR-3 in demagnetizing the magnets M. is correlated with an AC demagnetizing source which supplies a rapidly decreasing (tapered) alternating current to the magnets after they have been deenergized, in order to rapidly reduce the flux density of the magnets to substantially zero so that the cans can be deposited on the conveyor belt without hangup. This demagnetizing circuit is supplied by an isolation transformer T2 connected across the AC line. The secondary winding of the transformer T] which is connected across the DC magnet lines 160-162 in series with a conventional type electric lamp which is turned off by normally closed, simultaneously operating relay contacts SCR-2 and SCR-4.

The blade switch LS-2 (which is closed when the cans are brought up against the magnets), (FIGS. 6 and 7) and the carriage switch LS-3 (which is opened when the carriage C is retracted) are connected in series across the AC line with a control relay SCR which operates various contacts as will be described presently. A slave relay BCR is also connected across the AC line in series with a relay contact 3CR-5 which is operated by the relay 3CR just mentioned. The contact SCR-5 is normally open, but when it is closed by energization of relay coil 3CR it is timed to reopen about l.5 seconds afier 3CR is deenergized, thus giving SCR-3 time to short out the magnets before the AC demagnetizing current is turned on.

OPERATIONAL DESCRIPTION OF THE CIRCUIT The operational description of the circuitry will be explained in steps with reference to the operational diagrams of FIGS. 8-12.

START-FIG. 8

The pallet hoist carriage I00 has been lowered enough so that the cans 10 are clear of the magnets M and the carriage has been advanced over the pallet hoist. With these condi' tions, the blade switch LS-2 is open thereby deenergizing the relay BCR. The magnet frame 70 (FIG. 4) rests on angles 56 so that the signal lamp switch LSI is open and the signal lamp S is out. With LS-Z open because of the lowered cans, relay 3CR deenergized, normally open contacts SCR-l in the control power supply line I64 are open and no firing signal is applied to control lines 168, I70 for the SCR firing module F.

Under these circumstances there is no DC power applied to the magnets through the DC power lines I60, I61.

Also, with relay SCR thus deenergized, the contacts 3CR-5 in the supply line for the slave relay 8CR will have opened and relay SCR is thereby deenergized. As mentioned, the contact 3CR-5 just mentioned are timed to open (TO) a short time after they have first been closed by energization of relay 3CR followed by deenergization of relay 3CR, the purposes of which will be explained presently. With the slave relay UCR deenergized as just described, normally closed contacts (NC) 8CR4 and 8CR-2 are closed and the demagnetization resistance lamp 180 is on from AC supplied by the isolation transformer T2.

Finally, with 3CR deenergized, the silicon controlled rectifier SCR-3 (provided to conduct collapse current from the magnets M) is cut off and offers a very high resistance in both directions to current flow and hence does not short out the AC demagnetization current flowing through the lamp 180 via contacts 8CR-4 and SCR-2. SCR-3 is cut off at this time because when relay SCR was deenergized by contacts SCR-5 contacts SCR-3 which are normally closed (NC) short the gate of SCR-3 to the return or ground line 1660! the DC control circuit. This grounding of the gate of SCR-3 causes the latter to cut off as soon as the current therethrough reaches some minimum or holding value (e.g. 5-200 MA).

To summarize the conditions shown in FIG. 8, blade switch LS-Z is open, 3CR is deenergized, contacts JCR-I are open and no firing signal is applied to the control winding of the firing module. No direct current is applied to the magnets from the bridge, the silicon controlled relay SCR-3 is cut off to provide a very high resistance path in either direction, and the AC demagnetizing current has been applied through the rapidly heating lamp I80. The demagnetizing current will have been applied for a sufficient length of time to remove all the residual magnetism from the magnets, the time required being in the order of one-tenth second.

The switch I36 for the pallet hoist can now be operated to raise the pallet for presenting cans to the magnets for unloadmg.

RAISE I-IOIST-FIG. 9

In FIG. 9 the pallet hoist has been raised until the top tier of cans it) closes the blade switch LS-2, (FIG. 7broken lines). Slight additional raising of the hoist lifts the magnet frame and closes one or both limit switches LS-l (FIG. 1A) lighting the signal lamp S indicating that the switch 136 should be operated to stop the pallet hoist elevation. As mentioned, the two switches LS-l are in parallel but this connection is omitted in FIGS. 8-12 for clarity. These switches are set to close when their buttons are released. With the blade switch LS-Z closed, the relay SCR is energized through LS-Z and through the carriage retract switch LS-3, the latter being closed when the carriage is advanced to bring the magnets over the pallet. Contacts 3CR-5 now close, energizing the slave relay 8CR. 8CR now opens the normally closed contacts 8CR-4 and 8CR-2, turning off the demagnetization lamp 180 and removing the AC demagnetizing source across the magnets.

Energization of 8CR also opens the normally closed contacts 8CR-3 thereby disconnecting the gate of the silicon control relay SCR-3 from neutral and connecting the gate through resistance R2 to the positive control line 164. The application of the control voltage on the gate of SCR-3 readies SCR-3 for conduction.

Under the present invention, energization of relay SCR also closes normally open contacts 3CR-l in the control power line I64 thereby making signal current available to the control circuit. Tl-le positive line 168 of the control circuit for the control winding of the SCR firing module can be fed either through contacts 3CR-2 which are normally open and are timed to close about three seconds after 3CR is energized or through contacts SCR-3 which are normally closed and are timed to open about three seconds after 3CR is energized. The details of such a time are essential to the circuit and a pneumatic timer relay of this type is sold to the trade as the Allen Bradley Pneumatic Timer No. 700 NT, manufactured by the Allen Bradley Company of I201 South Second Street, Milwaukee, Wise.

Thus, when the relay 3CR is energized and normally open contacts SCR-l are closed as just described, current from the control line 164 is fed through contacts 3CR-l and tapped off from the surge potentiometer R5. This current is fed through the normally closed (but timed to open) contacts 3CR-3 to the control winding of the SCR firing module F. The potentiometer R5 will be set so that a surge signal current is applied which is higher than the normal signal current applied to the firing module control winding, in order that a higher then normal current will be supplied by the bridge to the magnets through the DC power lines 160, 162. The magnetic flux in the magnets is now higher than normal for initial gripping of cans and pulling slightly misaligned or tilted cans into place to form a precise pattern under the magnets.

When 3CR was energized the normally open contacts 3CR-2 in the hold" circuit started timing towards their closed position and the normally closed surge" contacts 3CR-3 now supplying the surge signal to potentiometer R5, started timing toward their open condition, but for the first 3 seconds (for example) of the operation just described, the condition will be as shown in FIG. 9.

The fact that gate SCR-3 is connected to a plus voltage so that it can conduct does not affect the power flow through the magnets. This flow will be through the bridge diodes and silicon controlled rectiliers and will not be shorted by SCR-3. SCR-3 will conduct now only in response to a pulsating field collapse current which exceeds that from the power supply bridge.

LOWER l-lOlST, RETRACT CARRIAGE-FIG.

immediately after the condition of FIG. 9 just described, the pallet control switch 136 is operated to lower the pallet and provide clearance between the pallet or cans thereon and the cans just picked up by the magnets. This will open the signal lamp switch LS-l and the signal lamp 5 will go out signifying that the carriage can be retracted without interference. The carriage switch 142 can be operated to retract the carriage by means of the four-way valve and the cylinder 92 as previously described. The cans themselves hold the blade switch LS-2 closed so that the magnets remain energized.

The relay 8CR remains energized through contacts 3CR-5 which will not start timing towards their open position until the relay 3CR is deenergized. The AC demagnetizing resistance lamp 180 remains off and SCR-3 is gated so that it can conduct, if required, by excessive magnetic field collapse currents that might occur in between power supply pulses.

Under the present invention, after about 3 seconds a lower current hold" signal is applied to the control winding of the SCR firing module and the higher current surge" signal is cut off. This is because the surge contact SCR-3 will have timed open, and the "hold" contact 3CR2 will have timed to close, and will supply a lower control current through the potentiometer R4.

In the circuit condition shown in FIG. 11 the carriage has been retracted and stopped over the conveyor belt 22 and the switch actuator 98 on the carriage has opened contacts LS3. Relay 3CR is now deenergized and normally open contacts SCR-l in the control power line 164 will open. Thus, no control signal is applied in lines 168, to the control winding of the SCR firing module and no DC power is applied to the magnets through the lines 160, 162. Thus the magnetic field is collapsing in the magnets. As explained in the aforesaid Albright et al. application, the collapse current is shorted out by SCR-3 which has been gated to conduct through R2 and the DC con trol power line 164.

Although the relay 3CR has been deenergized by the opening of carriage switch LS-3, the slave relay 8CR remains energized. This is because contacts 3CR-5 for relay 8CR have started timing toward their open position when JCR was deenergized but are still closed. Thus, with 8CR still energized the normally closed contacts 8CR-4 and 8CR-2 in the circuit of the demagnetizing lamp circuit I80 remain open and the lamp is off and no demagnetizing circuit during the period when SCR-3 is carrying the magnet collapse current.

DROP CANS-DEMAGNETIZING-FIG. 12

In FIG. [2, the magnetic field in the magnets has collapsed sufficiently so that they are demagnetized and the cans dropped. This indicates that the operator can advance the carriage by means of the control switch 142 for the carriage operating piston 92. Well within 1.5 seconds of the time when SCR3 was gated to conduct (FIG. 11), the rectifier SCR-3 will have conducted enough of the field collapse current to prevent large current pulses from feeding back into the rectifier bridge of the SCR firing module. After about 1.5 seconds have elapsed from the condition of FIG. l1 contacts 3CR-5 (which started timing toward their open position as soon as 3CR was deenergized) will have timed open and the slave relay 8CR is deenergized, as indicated in FIG. 12. This closes normally closed contacts 8CR-3 in the gate circuit of SCR-3 so that the gate of this relay is connected to neutral and SCR-3 is cut ofi. SCR now cuts ofi" because the collapse current soon reaches zero, although a substantial residual magnetic field R remains. With SCR-3 cut ofi it presents a very high resistance to current flow in both directions and hence will not short AC current flow between the DC magnet lines 160, 162 in either direction.

When 8CR is deenergized, contacts 8CR-4 and 8CR-2 revert to their normally closed condition and the AC demagnetizing lamp resistance is turned on via the isolation transformer T2. A rapidly tapering AC demagnetizing source is now applied to the magnets M and after about six cycles the magnets are fully demagnetized, as described and claimed in the aforementioned Albright et al. application. This insures that all the cans will drop onto the conveyor 32 because the residual magnetism or flux density of the magnets is now substantially zero.

As to component values, these can be selected in accordance with well known principles in electrical engineering. The Zener diode D5 is selected to limit the control signal voltage to that which is maximum of the control winding of the SCR firing module, e.g. 8 volts. This control winding being part of a magnetic amplifier in accordance with well known principles. The current limiting resistor R1 is selected to work with the Zener diode under well known principles. The limit rheostat R3 has been provided to prevent a signal on the control winding through either potentiometers R4 or R5 from exceeding a predetermined scale maximum and hence damage the SCR5 module. This potentiometer can be l,000 ohms. The hold and surge potentiometers in the example being given can be 2,000 ohms.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention as set forth in the appended claims.

What l claim is:

1. Apparatus for transferring paramagnetic articles such as cans between pallet means or the like and a conveyor, comprising a carriage and means for moving said carriage between positions overlying said pallet means and said conveyor, electromagnets on said carriage; a DC power source for said magnets comprising a full wave rectifier bridge having silicon controlled rectifiers in two legs and diodes in the other legs, an AC source connected between one set of legs and a DC supply for said magnets connected between the other legs; control means connected to the silicon controlled rectifiers of said bridge for varying the current supplied by the bridge to said magnets in accordance with a DC control signal; a DC control signal source, means connected to the latter for supplying a relatively high value DC surge current control signal and a lower value DC hold current control signal to said silicon controlled rectifier control means, main switch means for energizing said DC control signal source, and timer relay means controlled by said main switch means for initially connecting said surge control signal to said control means for the silicon controlled rectifiers, and for then replacing the surge control signal with said hold current control signal.

2. The apparatus of claim 1, wherein said DC control signal source comprises a stepdown transformer connected to said AC source and rectifier means connected to said stepdown transformer.

3. The apparatus of claim 1, wherein said means for supplying the DC surge and hold control signals to said silicon controlled rectifier control means includes a potentiometer for each signal connected to said DC control signal source.

4. The apparatus of claim 3, wherein said surge and hold current control means each include timer relay contacts con nected to the associated potentiometer.

5. The apparatus of claim 1, including elevator means for bringing the articles and said magnets together, said main switch means including a switch operator projecting down past the lower faces of the magnets for operation of said main switch directly by the articles as the articles and magnets are brought together.

(5/69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,599, Dated August 17, 1971 Inventor-( PETER L, CHORNEY It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

1,01. 7, line 4 after "are" insert --not-- w 301. 8, line 37, after "demagnetizing" insert --AC is applied to the magnets through the demagnetizing-- Signed and sealed this 9th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. Apparatus for transferring paramagnetic articles such as cans between pallet means or the like and a conveyor, comprising a carriage and means for moving said carriage between positions overlying said pallet means and said conveyor, electromagnets on said carriage; a DC power source for said magnets comprising a full wave rectifier bridge having silicon controlled rectifiers in two legs and diodes in the other legs, an AC source connected between one set of legs and a DC supply for said magnets connected between the other legs; control means connected to the silicon controlled rectifiers of said bridge for varying the current supplied by the bridge to said magnets in accordance with a DC control signal; a DC control signal source, means connected to the latter for supplying a relatively high value DC surge current control signal and a lower value DC hold current control signal to said silicon controlled rectifier control means, main switch means for energizing said DC control signal source, and timer relay means controlled by said main switch means for initially connecting said surge control signal to said control means for the silicon controlled rectifiers, and for then replacing the surge control signal with said hold current control signal.
 2. The apparatus of claim 1, wherein said DC control signal source comprises a stepdown transformer connected to said AC source and rectifier means connected to said stepdown transformer.
 3. The apparatus of claim 1, wherein said means for supplying the DC surge and hold control signals to said silicon controlled rectifier control means includes a potentiometer for each signal connected to said DC control signal source.
 4. The apparatus of claim 3, wherein said surge and hold current control means each include timer relay contacts connected to the associated potentiometer.
 5. The apparatus of claim 1, including elevator means for bringing the articles and said magnets together, said main switch means including a switch operator projecting down past the lower faces of the magnets for operation of said main switch directly by the articles as the articles and magnets are brought together. 